Current interrupting means



CURRENT INTERRUPTING MEANS Filed ,July 3, 1939 2 Sheets-Sheet 1 Nov. 25, 1941. E, J, sRoKA CURRENT INTERRUPTING MEANS Filed July 3, 1939 2"Sheets-Sheet 2 W w w .Wil/101:25: 1

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` wwmdffdf LLUJ, I IJ UNITED sTATEs PATENT oFFlcE CURRENT IN TERRUPTING MEANS Edmund J. Sroka, Chicago, lll., signor to Schweitxer & Conrad, Inc., ChicagogllLLa corporation of Delaware Application July 3, 1939, Serial No. 282,633

22 Claims. (Cl. 20o-117) My invention relates, generally, to electrical Protective devices, and it has particular relation to replaceable links to be used in connection with low current liquid fuses. 'I'he primary requirements of a replaceable link for fuses adapted to interrupt low amperage (i. e., a few hundredths of an ampere) currents are, that it be capable of withstanding high tension stress and at the same time will be releasable at a predetermined low overload current, and yet retain substantially uniform characteristics while operating at any capacity below that at which it is designed to operate. vIn fuse devices wherein solder or similar material is used to hold two parts together and which is melted to releaseV these parts, it is'often possible to bring the current almost up to Jthe point of operation without actually permitting the separation of the two parts, but thereby, mateiially altering the time-current characteristics of the circuit interrupting device. Such alteration is obviously undesirable since in effect it amounts to the enforced use of a variable characteristic device where a device of predetermined substantially constant characteristic is required. When a replaceable link is used in connection with liquid circuit interrupting devices, it is desirable that the surrounding liquid vapors or liquid will not appreciably aect the timing operation thereof. My invention provides a low current replaceable link meeting each and all of the above desirable requirements.

The object of my invention, generally stated, is to electrically interconnect terminals with a heater element, the heat from which melts a mechanical strain connection between the terminals which connection is not in circuit relationship with the terminals and which releases when a predetermined current flow is exceeded and which will not be substantially altered if this predetermined current flow is nearly but not quite reached.

Another object of my invention is the provision of terminals interconnected by a heater element the heat from which melts a m'echanical connection between the terminals that is out of the electrical circuit between them.

Another object of my invention is thelprovision of a strain element for a circuit interrupting device which is adapted to be ruptured by heat from a heater element.

Another object of myinvention is the provision of a. positive mechanical connection between the terminals of a replaceable link which is yet can be released at a predetermined overload I- l current.

Another object of my invention is the provision of terminals interconnected by a heater element the heat from which melts a mechanical connection between the terminals that is'out oi the electrical circuit therebetween and a strain wire conductor connected to one of the terminals which ruptures on a heavy overload.

Still another object of my invention is the `provision of a low current replaceable link for liquid fuses, the time-current characteristic of which will not be affected by the surrounding liquid vapors or liquid.

Other objects of my invention will, in part, be obvious and,in part, appear hereinafter.

Accordingly, my invention is disclosed in the embodiments thereof shownl in the accompany- 'ing drawings, and it comprises the features of construction, combination of parts, and arrangement of elements which will be exemplified in the constructions hereinafter set forth and the scope of the application of which will be indicated in the appended claims. v

For a more complete understanding of 'the nature and scope of my invention, reference may be had to the following detailed description,

taken in conjunction with the accompanying drawings in which:

Figure 1 is a vertical section through the upper end of a circuit interrupter' of the liquid typo illustrating the application of one embodiment of my invention thereto; v

Figure 2 is a vertical sectional view of a replaceable link illustrating another embodiment of my invention;

Figure 3 is a view in side elevation oi a replaceable link, similar to those sh'own in Figures 1 and 2with a strain wire connected in series circuit relationship;

Figure 4 is a vertical sectional rview of a replaceable link illustrating another embodiment l of my invention; and

Figure 5 is a vertical sectionalview of a replaceable link illustrating still another embodiment of my invention.

` With a view of illustrating the general nature of my invention, reference may now rbewhad to Figure l of the drawings wherein the reference character I0 designates, generally, a circuit interrupter of the liquid type utilizing a replaceable link Il which is constructed according to one embodiment of my invention. The circuit interrupter lo comprises a glass sleeve or housing 'capable of withstanding high tension stress and 55 I2 with an upper terminal ferrule I3 secured thereto by sealing alloy I4. The ierrule i3 may be closed at the top with a cap I5. terminal l5 of the circuit interrupting link projects through a 'conducting spider l1 and is secured thereto-by aclamping nut I3. A lower arcin'g contact |9 of the circuit interrupter I5 with pins 2n projecting therefrom is supported from the lower terminal 2|' oi the circuit interrupting link The arcing contact i9 is connected with the lower terminal (not sh'own) of thecircuit interrupter III through a exible conductor 22, the upper ends o! which are gathered together and held in a tubular socket 23 secured to the lower arcing contact |9 by.a screw head 24 as shown. In order to secure the immediate withdrawal of the arcing contact I9 wh'en the circuit interrupting link I I is operated. a strong tension spring 25 is secured at its upper end to an inwardly extending flange 25 carried in a groove 21 on the tubular socket 23. A'liquid director 28 is supported by the pins 25 fitting in a groove 29 as shown. The replaceable link is surrounded by a tube 30 depending from a mounting plate 3| carried from the upper iferrule I3 The circuit interrupter I0 is of the type shown in Figure 4 of UnitedStates Patent No. 2,091,430, dated August 31, 1937, to Conrad. It differs from the Conrad circuit interrupter in that my improved replaceable link is-provided between the arcing terminals. Since the circuit interrupter i0 has the same general operation as the bushings provided in the -ends thereof,v as shown. The sleeves 35 may be secured together by a thin deposit of solder 31 between the bushingsv 35. The solder 31 may be standard 50/50 solder or some other low melting point alloy as An upper cordingly, the shorttime rating or the replaceable link H is increased and the current value at which it is designed to blow is reduced.

In operation, wh'en the current flowing through the conductive. rod 39 exceeds the rated capacity of the replaceable link Il, sufiicient heat will be' radiated therefrom to melt the deposit -of solder 31. I'he opposing terminals I5 and I1 may then be separated by the spring 25 while the conductive rod 39 drops out or circuit relationship therewith. The sleeves 35 or insulation material provide eirective heat insulation for the rod 39, th'erebymaking the solder 31 relatively sensitive only to the heat within the circuitinterrupting link Il and relatively only slightly sensitive to the ambient temperature. That is, the liquid vapors and liquid of the circuit interrupter i0 have little eilect on the time-current characteristic of the replaceable link Il.

In Figure 2 of the drawings a replaceable link is shown generally at 45 which is or the same general construction as the link H except that the conductive rod 39 oi link is replaced with a different type of heater element. The replaceable link 45 comprises opposing terminals 45 and 41 with a pair oi' sleeves 48 projecting therefrom having metal bushings 49 at the juxtaposed Woodsmetal having the desired melting temperature. Coil springs 35 may be provided within the recesses 32 and 33 in the terminals |5 and 2| for supporting a conductive rod 39 therebetween. It is possible to eliminate one or both of the recesses 32 and 33 and one or both of the coil springs 39, but the preferred construction is as shown. The conductive rod 35 is provided with terminals formed by spraying copper thereon and it constitutes a connection between the opposing terminals I5 and 2|. The rod 39 may be made of carbon or similar conducting material with a resistance in the order o! 5 to l0- ends thereof. The sleeves 45 are secured together by a small amount of solder 50 therebetween. Reoesses may be provided in the opposing ends of the terminals 45 and 41 wherein coil springs 5| may be disposed for holding a heater element 52 therebetween. The heater element 52 comprises a wire 53 formed of suitable mal terial such as Nichrome and wound on a core 54 of insulating material such as lava and pro-JY With a view of providing what may betermed a dual functioning link embodying my invention, the construction shown in Figure 3 of the drawings may be used. A replaceable link is there shown generally at 55 comprising opposing terminals 5I and 52 with sleeves 53 projecting therefrom and provided with metal bushings 55 in the ends thereof and secured together by a mass o! solder 55.- The heater element provided withinthe sleeve 53'may be either that as shown for thelink Il in Figure 1 0l for the link 55 in Figure 2. 'Ihe lower terminal 52 is adapted to be securedto a terminal by a strain wire 51,- which is preferably a high strength' wire, such las Nichrome wire-having a current carrying capacity somewhat greater than the current carrying capacity ,of the fuse link 55. -When a short circuit occurs, the link 55 is shattered but, since g5 thisrequires a slight interval-of time, the cirterminals l5 and 2| 'which is out .ot circuit' relationship therewith. The `strength of this mechanical connection remains vsubstantially constant, not being altered by being nearly but not quite melted. It will be seen that the strength-oi.' this mechanical connection is proportional to the soldered area between the bushings 3 5. ASince the mass oi' solder 31 is small, it is quickly melted cuit is opened by the fusion of the strain wire 51 which, it`will be understood, takes placchefore the link 55 is shattered. On a relatively small overload, the solder 55 is melted first/by the.' beat which is generated by the relatively 4smallover-current. The bushings 55 then separate, whereupon the circuit is interrupted, The dual range of operation is `thus providedfon the one hand by th strain wire 51which arts whenits melting vtemperature is Acunder short circuit onditions and on the gther 'Il and Il are metallic, the operation of the cirhand by the solder between the bushings il which melts under relativelyslight or low overload conditions and allows them to part.

Referring to Figure 4 of the drawings, another embodiment of my invention is illustrated in connection with a replaceable link designated generally at 10 comprising upper and lower terminals ll and 12 having sleeves 'I3 of insulating material projecting therefrom and provided with metal bushings Il in the ends thereof. The sleeves "Il are secured together by a deposit of solder l between the metal bushings 14. The sleeves Il may be supported from the terminals 1| and 'I2 by pins 'Il passing therethrough as shown. In order to electrically interconnect the terminals 'Il and 12,.a heater element Il is provided therebetween whichmaybeofNichrome wire.

When the current carried by the link 1l exceeds y that of its rated capacity. sufiicient heat will be In theembodiments of the invention shown in Figures 1. 2, 3 and 4 a butt joint construction is provided between the metal bushings which are held together by a thin layer of solder. As

.soon as the solderis raised to its melting point,

the metal bushings are immediately separated.

l.This permits more accurate calibration of the cuit interrupting link Il tends to be erratic because of the fact that the metal sleeves Il and Il will pick up and radiate heat at various rates, depending upon the temperature of the gas or the liquid which surrounds the circuit inter-` f depend upon both the temperature of the oil and the current carried by the link.

When the links shown in Figures 1, 2, 4 and 5 are subjected to short circuit\conditions, the

' links are not intended to be limited in applicafuse links using this butt joint construction than is the case with a lap Joint as it will hereinafter appear. v p

In Figure 5 of the drawings still another embodiment of my invention is illustrated by a replaceable link shown generally at Il having conductors Il andl! secured in the reduced sections of ,tubular terminal members Il and N. The terminal members 8l and I4 carry insulating disks l5 and respectively, from which metal sleeves l1 and Il project toward each other in telescopic relation, as shown. The sleeve Il is somewhat smaller in diameter than sleeve Il and projects therein a short istance. A deposit of solder Il is provided between the interiltting portions of the sleeves l'l and I8 to secure them together. An insulating core II is provided` between the terminal members I3 and Il' on which a heater element ll, such as Nichrome'wire, may be wound to interconnect the conductors Il and l2.

In the event that the link Il carries more than its rated' capacity, suii'icient heat will be dissipated from theV heater element Il to nmelt the solder I! thereby permitting the separation of the terminal members I3 and Il. The heater element Il will be ruptured mechanically when the terminal members Il and Il are separated.

The embodiment of my invention illustrated by the link Il in Figure 5 does not appear to be as satisfactory, under certain operating condition to liquid circuitinterrupters. ,Howeven my improved links are particularly applicable to liquid circuitinterrupters since the surrounding liquid vapors or liquids do not appreciably affect the timing operation thereof. These links are particularly suitable for use in vconnection with potential transformer protection in which application the normal currents amount to onlya few hundredths of an ampere. H owever, if found desirable, they can be used for other applications and with other types of apparatus.

`Since certain further changes can be made vin the foregoing constructions and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter shown in the accompanying drawings or described hereinbefore shall be interpreted as, illustrative and not in a limiting sense.'

I claim as my invention:

1. In a circuit interrupter, in combination, a pair of relatively movable terminals biased for movement apart, means restraining movement apart of said terminals including a low melting point material out of electrical conducting relation between said terminals, and means for melting said material by radiated heat on flow of predetermined current between said terminals, there being an air space between said low melting point material and said melting means to retard the transfer of heat therebetween.

2. In a circuit interrupter, in combination, ay I pair ofvrelatively movable terminals biased for Amovement apart, means restraining movement between said terminals and adapted on flow oiv predetermined current therethroughto radiate sufficient heat to melt said material and thereby release said terminals for movement apart, there beingv an air space between said mass of low melting point material and said heater means receded from. Furthermore. sincevthe sleeves f to retard the transfer of heat therebetween'.

3. In a circuit interrupter, in combination, a

pair oi relatively movable terminals biased for movement apart, means restraining movement apartof saidy terminals including a small mass of low melting point metal and means for insulating the same from at least one of said terminals so 'as to prevent current. ow therethrough, heater means providing a current pathbetween said terminals and adapted on ilow of terminals, a sleeve member carried by and projecting from each of ,said terminals toward the opposite terminal, the ends of said sleeve mempredetermined current therethroughto radiate spring, strain means mechanically interconnecting said terminals including a small mass of low melting point material electrically insulated from the current path between said terminals and adapted in the solid state to withstand the tension of said spring, and electric heater means electrically interconnecting said terminals and .arranged and adapted to melt said low melting point material on now of predetermined current between said terminals whereby said spring is no longer restrained and said terminals are separated thereby, there being an air space between said mass of low melting point material and said ythe transfer of heat material electrically insulated from at least one of said terminals so that no current ilows therethrough, and a heater element electrically interbers being juxtaposed and secured togetherwith a small mass of low melting point metal, and a heater element within said sleeve members electrically interconnecting said terminals, said link being operated when said low melting point metal -becomes melted by heat from said heater element, and said low melting point metal being out of conducting relation between said terminals whereby the current ilowlng between said terminals does not ilow through said lowmelting point metal.

9. A replaceable link adapted to be tensioned by a spring comprising, in combination, a pair of terminals disposed to be biased apart by said spring, strain means mechanically interconnecting said terminals including a small mass oi low connecting said terminals, said link being operated when said low melting point material becomes melted by heat from said heater element.

6. A replaceable link comprising, in combination, opposing spaced apart separable terminals, a member carried by each of said terminals and projecting toward the opposite terminal, the ends of said members being juxtaposed and secured together with a small mass of .low melting point material in non-electrical conducting relation to at least one of said terminals, and a heater element electrically interconnecting said terminals, said link being operated when said low melting point material becomes melted by heat from said heater element, the material forming the interconnecting means between said separable terminals, excepting said heater element, including insulating material whereby all of the current ilow between said terminals takes place through said heater element.

melting point material having a relatively large cross-sectional area and being relatively thinand velectrically insulated from the current path between said terminals and adapted in the solid state to withstand thetension of said spring. and electric heater means electrically interconnecting said terminals and arranged and adapted to melt said-low melting point material on ow f predetermined current Y between said terminals whereby said spring is no longer restrained and said terminals are separated thereby.

105A replaceable link comprising, in combination, opposing spaced' apart separable terminals, amember of insulating material carried by each of said terminals and projecting toward the 0pf. posing terminal with. the ends thereof being4 juxtaposed, metal bushings provided on said juxtaposed ends and electrically insulated from said terminals by said insulating members, a small mass of solder between said bushings securing said members together, and a heater element electrically interconnecting said terminals, said link being operated when said soldervbecomes melted by heat from said heater element.

ll. A replaceable link adapted to be tensioned by a spring comprising, in combination, a pair of terminals disposed to be biased apart by rsaid spring, strain means mechanically interconnect- '1. A replaceable link comprising, in combina-- y tion, opposing spaced apart separable terminals, a member carried by and projecting from Veach of said terminals toward the opposite terminal, the ends of said members being juxtaposed and securedtogether with a small mass of solder in non-electrical conducting relation to at least one of said terminals, and a heater element electrically interconnecting said terminals, said link being operated when said solder becomesmelted by heat from said heater element.

.8, A circuit interrupting link' comprising,in combination, opposing spaced apart separable ing said terminals including a small mass of' low melting point material electrically insulated from the current path between said terminals and adapted in the solid state to withstand the tension of said spring, and electric heater means electrically interconnecting said terminals and arranged and adapted to melt said low melting point material on flow of predetermined current between said terminals whereby said spring is no longer restrained and said terminals are separated thereby, -sald electric 4heater means being unattached to at least one of said terminals whereby upon fusion of said low melting point material said terminals are mechanically free to be separated.

l2. A replaceable link comprising, in combination, opposing spaced apart separable terminals,

a recess' provided in the end of at least one of said opposing terminals, sleeve members of insulating material carried by each of said terminals and projecting toward the opposing terminal with the ends thereof being juxtaposed, metal bushings on said juxtaposed ends, a small mass of solder between said bushings securing said sleeve members together, resilient means in said recess, and .a heater element disposed within said sleeve members electrically interconnecting said terminals, said resilient means holding said tion, opposing spaced apart separable terminals,

recesses provided in the ends of each of said opposing terminals, a sleeve member of insulating material carried by each of said terminals and projecting toward the opposing terminal with the ends thereof being juxtaposed, metal bushings provided on saidjuxtaposed ends, a small mass oi solder between said bushings securing said sleeve members together, compression spring means in said recesses, and a heater element disposed within said sleeve members electrically interconnecting said terminals, said compression spring means holding said heater element in position to complete an electrical circuit between said terminals, and said link being operated when said solder becomes melted by heat from said heater element.

14. A replaceable link comprising, in combination, opposing spaced apart separable terminals, recesses provided in opposing ends of said terminals, a sleeve member of insulating material carried by each of said terminals and projecting toward" the opposing terminal with the ends thereof being juxtaposed, metal bushings provided on said juxtaposed ends, a small mass of solder between said bushings securing said sleeve members together, compression springs in said recesses, and a conductive rod disposed within said sleeve members between said compression springselectrically interconnecting said termi.- nals, said link being operated when said solder becomes melted by heat from said conductive rod.

15. A replaceable link comprising, in combination, opposing spaced apart separable terminals, recesses provided in opposing ends of said terminals, a sleeve member of insulating material carried by each of said terminals and projecting toward the opposing terminal with the ends thereof being juxtaposed, metal bushings provided on said juxtaposed ends, a small mass of solder between said bushings securing said sleeve members together, compression springs in said recesses, a heater element comprising a conductive wire wound on a core of insulation and connected t conductive caps on the ends of said core disposed within said sleeve members between said compression springs and electrically interconnecting said terminals, said link being operated when said solder becomes melted by heat from said heater element.

of fusible metal permitting separation oi' said 16. A replaceable link adapted to be tensioned by a spring comprising, in combination, a pair of terminals disposed to be biased apart by said spring, strain means mechanically interconnecting said terminals including a small mass of low melting point material electrically insulated from the current path between said. terminals and adapted in the solid state to withstand the tension of said spring,.e1ectric heater means electrically interconnecting said terminals and arranged and adapted to melt said low melting point material on flow of predetermined current between said terminals whereby said spring is no longer restrained and said terminals are separated thereby, and a fusible element in series circuit relation with said heater means adapted to blow on flow of relatively heavy overload current.

17. A replaceable link in combination, opposing spaced apart separable terminals, a sleeve member carried by each of said terminals and projecting toward the opposite terminal,

the ends of said sleeve members being juxtaposed and secured together with a small mass of solder, a heater element within said sleeve members electrically interconnecting said terminals, and a strain wire connected to one of. said separable terminals, said link being normally operated when said solder becomes melted by heat from said heater element, and in case of a heavy overload said link being operated by blowing of said strain wire.

18. A replaceable link comprising, in combination, opposing spaced `apart separable terminals, a sleeve member of insulating material carried by each of said terminals and projecting toward the opposing terminal with the ends thereof being juxtaposed, \metal bushings provided on said juxtaposed ends and electricallyinsulated from said terminals by said insulating members, a anali mass of solder between said bushings securing said sleeve members together, and a heater element of coiled wire disposed within said sleeve members and connected to said terminals, said link being operated when said solder is melted by heat from said heater element.

19. A replaceable link comprising, in combination, opposing spaced apart separable terminals, a metal sleeve member insulated from and carried by each of said terminals and projecting toward the opposing terminal, the end of one of said metal sleeve members tting within the other metal sleeve member, a small mass of low melting point material between the inter'tting portions of said metal sleeve members for hold ing the same against separation, and a heater element interconnecting said terminals and disposed within said metal sleeve members, said link being operated when said low melting point material is melted by heat from said heater element.

20. In a fuse, in combination, separable terminals, and means interconnecting said terminals and preventing the same from separating including fusible means adapted to be melted by heat generated by flow of relatively high overcurrent between said terminals and means providing a butt joint construction held inseparable by a relatively thin layer of fusible metal adapted to be melted by heat generated by flow of relatively low overcurrent between said terminals, the melting either of said fusible means or of said layer 21.'In a fuse, in combination, separable tenminals, and means interconnecting said terminals and preventing the same from separating including means having relatively low thermal capacity adapted to be melted only by heat gen-` erated by'flow of relatively high overcurrent between said terminals and a pair of abutting metallic members having relatively high thermal capacity and secured together by a relatively thin layer of fusible metal which is adapted to be melted by heat generated by flow of relatively low overcurrentl between said terminals, said low thermal capacity means and said pair of metallic members being connected in series between said terminals whereby' the same are permitted to separate on melting either oi?v said low thermal capacity means or of said layer of fusible metal.

22. In a fuse, in combination, separable terminalsj and means interconnecting said terminals and preventing the same from separating includ- 6 assaut ing means having relatively low thermal capacity adapted to be melted only by heat generated by flow of relatively high overcurrent'betweenrsaid y adapted to be melted by heat generated by ilow of relatively low overcurrent between said terminals, said low thermal capacity means and said pair of metallic members being connected in series between said terminals whereby the same are permitted to separate on melting either of saidI low thermal capacity means or of said layer of fusible metal.

. EDMUND J.`SRO KA. 

